1. Field of the Invention
The present invention relates to an inner tub for a washing machine, and particularly, to an inner tub for a washing machine by which a spin-drying of high speed can be made.
2. Description of the Background Art
Generally, washing machines can be divided into clutch driving type and direct drive type. Herein, the clutch driving type is a method for transmitting a driving force generated from a motor to a pulsator using a belt, pulley, and clutch, and the direct drive type is a method for driving a washing machine directly by connecting the driving motor to the washing motor.
FIG. 1 is a cross-sectional view showing a direct drive type washing machine according to the conventional art.
The conventional direct drive type washing machine comprises: a case 102 with an opened upper part; an outer tub 104, in which wash water is filled, supported inside the case 102; an inner tub 106 installed in the outer tub 104 so as to be rotatable for washing laundries; and a driving motor 110 installed on lower side of the outer tub 104 for rotating the inner tub 106 through a rotating shaft 108.
As shown FIGS. 1 and 2, the inner tub 106 comprises: an inner tub body 112 of cylindrical shape having a predetermined space in which the laundries are filled; an inner tub base 114 formed to make a bottom surface of the inner tub body 112 and having a pulsator 120 formed integrally or connected rotatably therein for making a wash water flow; and an inner tub hub 116 mounted on an outer surface of the inner tub base 114 for coupling the rotating shaft 108.
Herein, as shown in FIG. 3, a wash water circulating hole 122 through which the wash water passes is formed on a center of the outer surface of the inner tub base 114, and a groove 124 is formed so that the pulsator 120 is formed in radial direction centering around the wash water circulating hole 122.
As shown in FIG. 4, the inner tub hub 116 is formed as a triangle coupled to the outer surface of the inner tub base 114, a rotating shaft coupling hole 126 to which the rotating shaft 108 is coupled is formed on a center of the inner tub hub, and a plurality of supporting ribs 128 are formed as a radial shape centering around the rotating shaft coupling hole 126 in a circumferential direction. in addition, a plurality of bolt coupling holes 130 are formed on the outer side of the inner tub hub 116 for coupling to the inner tub base 114 using bolts.
In addition, in the conventional washing machine described above, the inner tub hub is formed as a triangle to couple the rotating shaft, however, the inner tub hub is not able to support the inner tub 106. Therefore, the rotation at high speed of the inner tub can not be made, and the spin-drying speed can not be increased. Thereby the spin-drying efficiency is lowered, and the dried degree of the laundries is also lowered.
That is, in order to increase the dried degree of the laundries, the spin-drying speed should be increased. However, in case of increasing the spin-drying speed, the centrifugal force is increased and stress applied to the inner tub is also increased, and thereby, reliability of the washing machine is lowered and vibration and noise are caused. Especially, it is difficult to increase the spin-drying speed more than a certain degree in a large capacity washing machine.